1. Field of the Invention
The present invention relates to an electronic device capable of transmitting data via an HDMI (High-Definition Multimedia Interface), a method for responding to a message, and a program.
2. Description of the Related Art
In recent years, the HDMI has been recognized as a standard enabling digital output from an AV (Audio Video) device, such as a DVD (Digital Versatile Disc) player or an STB (Set Top Box), to a display device, such as a digital TV (Television) set. The HDMI standard utilizes TMDS (Transition Minimized Differential Signaling) as a method for unidirectionally transmitting uncompressed digital video signals and digital audio signals and defines CEC (Consumer Electronics Control), which is a protocol for bidirectionally transmitting control signals. The use of the CEC protocol enables relay of control signals between devices, so that a plurality of AV devices can be controlled from a single remote control.
In the CEC protocol, physical addresses of respective devices are mapped first by using a DDC (Display Data Channel) bus. In this case, the respective devices obtain physical addresses by reading EDID (Extended Display Identification Data) from a device connected on the other end (sink device) through the DDC bus when an HPD (Hot Plug Detect) signal is “High”, that is, when the above-described unidirectional transmission is permitted to the sink device. Then, logical addresses of the respective devices are mapped by using a CEC bus. In this case, the respective devices transmit a <Polling> message and obtain a logical address in accordance with the response result (see Nonpatent Document 1: “High-Definition Multimedia Interface Specification Version 1.3a” Jun. 22, 2006).
However, Nonpatent Document 1 does not define message transmission using the CEC protocol in the case where connection permission by the HPD as a trigger to enable the above-described unidirectional transmission is canceled about a mapping state of physical and logical addresses.
On the other hand, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2007-202115 (paragraph [00] and drawings)) describes the following. A communication device holds obtained physical and logical addresses, and responds to a received message on the basis of the physical and logical addresses held therein regardless of whether connection permission by the HPD is effective or ineffective.